DESCRIPTION: Phagocyte motility is critical for neutrophil (PMN) and monocyte participation in the inflammatory response. Integrated interaction of F-actin based microfilamentous and microtubule (MT) based microtubular cytoskeletal controls phagocyte motility. Preliminary studies originating with a patient's immotile PMNs which had F-actin rich, hair-like surface projections, and defective actin polymerization led to description of new disease, NAD47/89, with increased amounts of LSP1, as actin binding protein. LSP1 is a leukocyte phosphoprotein with only 1 actin binding site, which is regulated in its ability to bind F-actin and inhibit actin polymerization in vitro. Despite having only one actin binding site, LSP1 bundles F-actin in cells, when increased it creates an interlaced F-actin network which forms F-actin rich- hair like projections on cells and it co-sediments with MT and co-localizes with MT and F-actin in phagocytes. The Applicant hypothesizes LSP1 forms a critical, phosphorylation regulated MT-to-f-actin link in phagocytes which regulates integrated (MT and F-actin) cytoskeletal structure and motile function of phagocytes. The proposal;s specific aims are:) to determine the effect of LSP1 absence and presence in varied dose, in cytoskeletal structure and motility of phagocytes. Natural LSP1- cells and LSP1- cells stably transfected and expressing LSP1 CDNA and LSP+ cells rendered LSP-by antisense will be examined for a range of motile function thought to require integrated cytoskeletal activity; 2) to determine the role of myristoylation, MT binding, self association and heterologous complex formation with 90 and 180 Kd proteins and LSP1 subdomains in creating LSP1's F-actin bundling activity; 3) to determine the role of LSP1 phosphorylation n regulating self association, F-actin bundling activity and MT-1-to-actin linkage in assembly of multi-molecular complex in vitro. The results will elucidate the function and regulation of LSP1 in phagocytes.